This invention relates generally to fittings coupled to tubes by swaging and more particularly to internal swage fittings.
A fitting is an auxiliary piece of equipment used to establish a terminus or junction site for a pipe, rod, or tube. In particular, a common use for a fitting is to connect separate tubes together to allow fluid to pass between, preferably without leakage. A fitting is also often used as a closure device to terminate the end of an otherwise open tube. Among many other applications, fittings are used in the aerospace industry to enclose tubes that convey fuel, hydraulic fluids, and the like from one location to another. In those and other critical applications, it is important that the fitting be sufficiently secure about the tube so as to withstand vibration, fluid characteristics and the like without failure.
Fittings are often coupled to tubes by welding. Welding can be a time-consuming, costly method of fitting affixation. Further, the weld may not be sufficient to ensure complete coupling and can cause unacceptable stress intensification factor of the tube. Swaging is an alternative mechanical process to join a fitting to a tube without the limitations associated with welding. There are two types of swaging processes: external swaging and internal swaging. External swaging involves the application of a fitting having external surface variations, such as radial or axial lands and grooves, to a tube. The applied fitting is swaged by forging, hammering, or squeezing, such that the external surface configuration is transferred to the interior of the fitting and thus to the tube. The tube is thereby deflected and contorted in the area where it contacts the fitting such that there is a secure coupling of the two. Unfortunately, the transfer of the fitting""s external surface configuration may not be sufficient to establish an adequate coupling, or may cause tube cracking in high cycle fatigue.
Internal swaging addresses, in part, some of the problems associated with external swaging. Internal swaging involves the application of a fitting having internal surface variations, again such as lands and grooves, to a tube. The applied fitting is swaged by placing an expander device within the tube and forcing the tube outwardly onto the interior surface of the fitting, or by squeezing the fitting onto the tube. There is a more direct interface between the fitting""s surface configuration and the tube exterior than exists with external swaging. The tube therefore generally conforms more closely to the original surface configuration, resulting in an improved connection between the fitting and the tube.
One type of internal swage fitting found to be suitable for some aerospace applications is described in U.S. Pat. No. 4,844,517 issued to Beiley et al. and assigned to Sierracin Corporation of Burbank, Calif. In one configuration, the Beiley fitting includes three or more radial rectangular grooves of specified width and depth dimensions. The groove closest to the end of the tube is of the same design as the other grooves. In another configuration, a series of ramped grooves are combined with a rectangular xe2x80x9cendxe2x80x9d groove. The rectangular end groove is substantially the same as the rectangular grooves of the first fitting configuration described. That is, the tube butts against it.
In commercial use, the Beiley fitting is most suitable for the swaging of tubes made of low ductility material, including Titanium. However, materials of relatively higher ductility, such as stainless steels including SS321, Inconel 625, and other similarly ductile materials, are also used in a wide array of tube applications, including aerospace fluid transfer systems. The materials of higher ductility xe2x80x9cflowxe2x80x9d to a greater extent than the lower ductility materials under equivalent swaging pressure. The swaging process performed on a low-ductility tube causes the tube to be drawn into the fitting and results in a bulging of the tube at the end groove. The flowing material is forced outwardly toward the fitting, placing significant axial load in that localized area. This bulging of the tube material can cause failure of the fitting as well as undesired changes in tube dimensions.
In order to account for the flowing or xe2x80x9csucking inxe2x80x9d of the tube into the fitting during the swaging process, it is necessary to set the tube back in relation to the fitting. That is, the tube must be placed in an offset position with respect to the fitting terminus to accommodate the axial and radial flow of the tube material. The swaging process causes the tube to flow and fill into the fitting to make up the setback difference. Since the tube must be completely and securely affixed to the fitting, maintaining the correct setback accurately is important. That is achieved by applying a capture collar about the tube adjacent to the fitting location. The collar must be rigidly but releasably affixed about the tube. Upon completion of the swaging process the collar must be removed. The steps of accurately aligning and applying and removing the collar must be repeated for each fitting applied to each tube of relatively ductile material. Therefore, what is needed is an internal swage fitting that can be used with ductile tubing. What is also needed is such an internal swage fitting that eliminates the need for setback and the use of a setback collar.
The above-mentioned needs are met by the present invention, which provides an internal swage fitting that accommodates the flow of high-ductility tube materials. The fitting includes a hollow cylindrical body having an internal surface and an external surface, a tube receiving region and a tube connection region. The internal surface of the body in the tube connection region includes one or more grooves and an expansion cavity for receiving excess material of the tube during a swaging process. The fitting also includes a tube stop wall adjacent to the expansion cavity. A termination end of the tube abuts the tube stop wall when the tube is placed within the cylindrical body. The expansion cavity includes an end wall extending from the tube stop wall and away from the one or more grooves at an angle so as to establish a fill space region for flowing tube material to fill in without applying excessive axial pressure on the fitting.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.